The present invention relates generally to welding machines and, more particularly, to a method and apparatus of communicating control signals to a welding power source from a remote location. Specifically, the invention relates to a power source whose operation is governed by control signals provided by a controller in response to command signals received across the weld cables connecting a wire feeder to the power source. In this regard, a voltage potential is not created between the secondary output of the power source and the wire feeder until a power-up command is transmitted to the receiver across the weld cables by the transmitter.
MIG welding, formerly known as Gas Metal Arc Welding (GMAW), combines the techniques and advantages of TIG welding's inert gas shielding with a continuous, consumable wire electrode. An electrical arc is created between the continuous, consumable wire electrode and a workpiece. As such, the consumable wire functions as the electrode in the weld circuit as well as the source of filler metal. MIG welding is a relatively simple process that allows an operator to concentrate on arc control. MIG welding may be used to weld most commercial metals and alloys including steel, aluminum, and stainless steel. Moreover, the travel speed and the deposition rates in MIG welding may be much higher than those typically associated with either Gas Tungsten Arc Welding (TIG) or Shielded Metal Arc Welding (stick) thereby making MIG welding a more efficient welding process. Additionally, by continuously feeding the consumable wire to the weld, electrode changing is minimized and as such, weld effects caused by interruptions in the welding process are reduced. The MIG welding process also produces very little or no slag, the arc and weld pool are clearly visible during welding, and post-weld clean-up is typically minimized. Another advantage of MIG welding is that it can be done in most positions which can be an asset for manufacturing and repair work where vertical or overhead welding may be required.
A wire feeder is operationally connected to the power source and is designed to deliver consumable wire to a weld. To further enhance the operability of the wire feeder of a MIG welding system, known welding systems have connected the power source and the wire feeder to one another such that control signals defining the operational parameters of the power source are transmitted or fed back from the wire feeder to the power source, generally referred to as remote control.
One type of remote control device is used to regulate the output voltage, current, and switch the welding power source output ON and OFF as well as change the power source mode via a pendant that connects to the power source by a multi-conductor cable. The solution is schematically illustrated in FIG. 1A. A wire feeder 2A is connected to a power source 4A by a control cable 6A that includes a 14-pin connector. The cable 6A used to transmit operational information to, and in some cases from the power source, may incorporate 2 to 14 conductors depending on how many functions are to be controlled. Separately connected between the power source 4A and wire feeder 2A is a high voltage weld cable 8A that delivers power to the wire feeder and creates a voltage potential between an electrode and a workpiece.
A significant drawback to this cable-based control is that the control cable is typically fragile relative to the welding cables designed to carry high currents at high voltages. Welding machines are commonly used at construction sites or shipyards where it is not uncommon for the welding machines to be periodically relocated or surrounded by other mobile heavy equipment operating in the same area. As such, the remote control cable can become damaged by being crushed or snagged from contact with surrounding machines and/or traffic. This can cause damage to the wire feeder and/or the welding power source if internal power conductors become shorted to signal leads that are connected to sensitive signal level circuitry.
One known system is a voltage following or voltage sensed wire feeder having an internal contactor. This solution is schematically shown in FIG. 1B. As shown, this system includes a wire feeder 2B that receives its electrical power from the voltage present in the welding circuit. The wire feeder is connected to a power source 4B via a weld cable 8B. With this system, the operator sets a desired welding current at the power source 4B and the wire feeder 2B regulates the arc voltage by increasing the rate wire feed is fed if the arc voltage increases and reduces the wire feed rate if the arc voltage decreases in order to maintain a constant arc voltage. One disadvantage of this system is that the operator has no convenient way to adjust the output of the welding power source to compensate for changes in workpiece thickness and/or fit up. The operator may call another person more conveniently located to the power source with a radio or some other means of communication to make the adjustment; however, if the operator is working alone, s/he must return to the power source to make the necessary adjustments. Another disadvantage of this system is that it requires the presence of a high current DC contactor to de-energize the welding circuit at the wire feeder. These contactors are large, heavy, costly, and require periodic maintenance to ensure proper and continual operation. The location of the secondary contactor in the remotely located wire feeder also requires that the welding circuit from the welding power source to the wire feeder remain energized even when not welding so that power is available to the wire feeder and welding arc when the gun trigger is activated. Accordingly, an open circuit voltage remains present across the weld cables. The weld cables, however, can become damaged at a worksite resulting in an unwanted arc being formed between an exposed portion of the cable and an unexpectant ground.
Referring now to FIG. 1C, another remote controlled system includes a radio transmitter type remote control. This approach has several disadvantages. First, electric arc welding can create radio frequency interference that negatively affects the communication between a transceiver 9A of the wire feeder 2C and the transceiver 9B of the power source 4C. Second, if the system is used inside metal structures such as tanks, ships, or large aircraft, the radio link can be lost due to the shielding effect of the metallic surroundings. Third, if multiple welding stations use a radio link for remote control, each control loop would require a separate security code to prevent cross-talk or mis-transmission of control signals to the wrong welding machine.
It is therefore desirable to design a remotely controlled welding machine that receives command signals from a wire feeder across a weld cables such that an open circuit voltage is not created between the secondary output of a power source and the wire feeder when the wire feeder is not supplying consumable wire to a weld. It would also be desirable to design a wire feeder absent a separate contactor assembly.